This invention relates to an improved hydraulic power tilt and trim device and more particularly to an improved tilt and trim device for an outboard drive.
It is generally the practice in marine outboard propulsion units such as outboard motors or the outboard drive portion of an inboard/outboard drive to provide a hydraulic cylinder assembly that is interposed between the outboard drive and the transom of the associated watercraft. This cylinder assembly can be pressurized by a pressure source for effecting not only trim adjustment but also for tiling the outboard drive up out of the water when not in use. In addition to these purposes, the cylinder includes a damping mechanism so that once in a trim adjusted position and if an underwater obstacle is struck, the outboard drive is permitted to pop up to clear the underwater object and then return to its trim adjusted position once the underwater obstacle has been cleared.
As is well known, the trim adjustment of the outboard drive is normally made when the watercraft is traveling in a forward mode and frequently at high speeds and/or high propulsion thrust. Hence, the hydraulic cylinder must be capable of providing large forces. Tilt-up operation of the outboard drive is, however, normally done when stationary and the amount of force required to effect the tilt-up motion is substantially less than when adjusting trim under power. Also, it is desirable to achieve the tilt-up motion in such a manner at more rapid rate than the trim adjustment.
Therefore, devices have been proposed that include a tilt cylinder that performs the tilt-up operation and a separate trim cylinder for achieving the trim operation. Frequently, there may be provided a pair of trim cylinders and a single tilt cylinder for a total of three cylinders. Obviously, these devices become quite complicated and complex.
In addition, there is the necessity of providing and driving electric motor, a fluid pump and a fluid reservoir for supplying the hydraulic fluid to the cylinders.
There are a number of advantages, particularly with small displacement engines to have a compact nature a compact construction that can be nested between the clamping bracket and the swivel bracket. However, when this is done, the position of the components is such with the prior art type of constructions that the cross-sectional area of the trim cylinder is adversely effected.
In order to improve the compactness of the arrangement, there have been proposed telescopic tilt and trim devices wherein the outer cylinder housing defines a cavity in which a hollow trim cylinder is supported for reciprocation. A tilt piston is slidably supported within the trim cylinder and has a piston rod that is connected to one of the outboard drive or watercraft with the outer cylinder being connected to the other. With these types of arrangements, it has been the practice to have the seal for the trim cylinder and hence its effective area being disposed at the lower portion of the cylinder. However, this is normally adjacent where the fluid pump and fluid reservoir are and this limits the maximum effective diameter due to the aforenoted spatial requirements.
It is, therefore, a principal object of this invention to provide a tilt and trim cylinder that can have a large effective area and yet still provide a compact assembly.
It is a further object of this invention to provide an improved compact tilt and trim arrangement for an outboard drive.
The problems with the prior art type of construction can be best understood by reference to FIGS. 1 and 2-6. FIG. 1 is a cross-sectional view taken through a prior art type of construction, which is indicated generally by reference numeral 21. FIGS. 2-6 are schematic cross-sectional views showing the operation of the unit from the fully trimmed tilted down position of FIG. 2 to the fully trimmed up position of FIG. 4 and finally to the fully tilted up position of FIG. 6.
The construction of the arrangement will be described first by reference to FIG. 1 in which it can be seen that the device 21 includes a cylinder assembly 22 that is provided with a cylinder bore 23. This cylinder bore 23 defines an internal chamber 24 that is closed at its lower end by an integral wall and which is closed at its upper end by a combined end closure and gland 25. The cylinder assembly 22 is adapted to be connected to either of the outboard drive or the transom. In the illustrated arrangement the cylinder is attached to the transom in a manner which will be later described in conjunction with the description of the preferred embodiment of FIG. 7. To this end, the cylinder is provided with a trunnion 26 that defines a bore 27 to receive a pivot pin for pivotal connection to the transom.
A trim cylinder, indicated generally by the reference numeral 28 is slidably supported within the cavity 24 and has an internal bore 29. The trim cylinder 28 has on its outer periphery a cylindrical groove 31 formed at its lower end that receives an O-ring seal 32 so as to effect sealing with the cylinder bore 23 of the outer cylinder assembly 22.
A piston 33 is slidably supported within the cylinder bore 29 of the trim cylinder. This piston 34 is affixed to a piston rod 31 that extends through the gland 25 and has a trunnion 35 at its upper end. The trunnion 35 affords a means of attachment to the other of the transom and outboard drive and in the illustrated embodiment this attachment is to the outboard drive. A bore 37 extends through the trunnion 35 to receive a pivot pin for this connection.
A combined gland and closure member 38 is suitably affixed to the upper end of the trim cylinder 28 and through which the piston rod 34 extends. This closure 38 carries a position responsive valve 39 which functions in a manner to be described.
Positioned within the cylinder bore 29 of the trim cylinder 28 below the piston 35 is a floating piston 41. The floating piston is held in a lowermost position by means of a snap ring 40 that is contained in a groove at the lower end of the trim cylinder 28.
A shock absorber valve 42 is provided in the piston 33 for permitting flow from a chamber 43 formed above the tilt piston 33 and the cylinder bore 29 to a chamber 44 formed therebelow which chamber is defined by the upper surface of the floating piston 41. Fluid flows in this direction, in the manner to be described, when an underwater obstacle is struck.
Once the underwater obstacle is cleared, the tilt piston 33 can move back to its trim adjusted position by displacing fluid from the chamber 44 back to the chamber 43 through a let-down check valve 45 also positioned in the piston 33.
The hydraulic tilt and trim control is provided by pressurizing the chamber 24 below the trim cylinder 28 and floating piston 41 or exhausting this area to return through a passage 46 formed in the cylinder 22 at the lower end of the cylinder bore 23. A further passage 48 is formed at the upper end of the cylinder bore 23 and communicates with an area above the trim cylinder 28 adjacent the gland enclosure 25. This communicates with the chamber indicated by the reference numeral 47. The ports 46 and 48 may be pressurized or vented with the flow occurring in the direction of the double-headed arrows 49 in FIG. 1.
As should be readily apparent, the fact that the O-ring seal 32 is provided at the bottom of the trim cylinder 38 and thus determines its maximum diameter limits the overall diameter of the assembly. As will become apparent by reference to FIGS. 8 and 9 of the preferred embodiment, this is the area adjacent the reservoir and fluid pump and this limits the effective force that can be exerted for trimming operation.
In addition to the aforenoted advantages, because the seal between the trim cylinder and the outer cylinder housing is at the lower end of this housing, then a long tool and intricate machining operation is required. Since it is desirable to maintain close tolerances in this area, this difficulty in machining gives rise to added costs for the prior art type of constructions.
The operation will now be described by particular reference to the FIGS. 2-6 of the drawings. FIG. 2 shows the condition when the outboard drive is in its fully trimmed fully tilted down position. In this condition, the trim cylinder 28 is at the bottom of the cylinder bore 23 and the tilt piston 23 is engaged with the floating piston 41 which is at its lowermost position as determined by the position of the snap ring 40.
If it is desired to effect trim-up operation, the hydraulic circuitry associated with the system is operated so as to pressurize the chamber 24 through the port 46 and open the port 48 to act as a return port. This hydraulic pressure in the chamber 24 will act on the floating piston 41 and trim cylinder 28 so as to cause the floating piston 41, piston 33, and piston rod 34 to move upwardly, as shown in FIG. 3. This will effect a trim operation on the outboard drive. Also, since the effective cross-sectional area of the trim-up portion of the piston operation is relatively large, there will be a high trim-up force and relatively large displacement of fluid in order to achieve this operation at a relatively low speed. This is done because the system operates against the driving thrust of the propulsion unit under most trim adjustment positions.
The trim adjustment can be stopped in any position, and when this is done, for example, if it is discontinued at the position shown in FIG. 3, this will be the new trim adjusted position. In this condition, if an underwater obstacle is struck with sufficient force, the piston rod 34 will be drawn upwardly and the absorber valve 42 will open so that fluid can flow from the chamber 43 through the piston 33 to the area between the piston 33 and the floating piston 41. When the underwater obstacle is cleared, the weight of the outboard drive will cause pressure on the piston 33 to move downwardly, and the fluid can return to the chamber 43 through the light let-down valve 45, as is well known in this art.
FIG. 4 shows the operation necessary to achieve complete trim up, and under this condition the trim cylinder 28 will move to the position shown in FIG. 4, at which time the position responsive valve 39 will be opened. This is necessary to achieve final tilt-up operation if this is desired.
FIGS. 5 and 6 show how tilt-up operation is achieved, and this is done by continuing to pressurize the chamber 24 below the trim cylinder 28. Since the trim cylinder 28 is at the end of its stroke, the fluid pressure will act in the cylinder bore 23 of the trim cylinder 28 and on the floating piston 41, which will be forced into abutting relationship with the piston 33 and move the piston rod 34 and outboard drive unit upwardly. When this happens, fluid is displaced through the position responsive valve 39 and port 48 back to the suction side of the pump. Since the floating piston 41 has less effective area than the trim piston 28, this tilt-up operation will be at a higher rate of speed but will be done with less force. However, since the driving thrust need not be resisted, this presents no problem.
FIG. 6 shows the fully tilted up position, and in this position it should be noted that the piston 33 bottoms against the closure at the end of the trim cylinder 28.
A disadvantage of this construction is that the position responsive valve 39 will be retained in the open position, and hence, the pressure in the upper chamber 47 may exceed the pressure in the lower chamber 24, and a force will be applied due to the weight of the outboard motor that can overcome the frictional drag of the O-ring seal 32 (FIG. 1) and cause the arrangement to drift downwardly. This same action may occur when operating in reverse mode or when maintenance work is made on the lower unit with the lower case removed or when disassembled in the factory. Said another way, it is desirable to retain the trim piston 28 in its fully up position as shown in FIG. 6 in many instances, and the prior art constructions simply do not make this possible.
It is, therefore, a still further object of this invention to provide an improved tilt and trim hydraulic device wherein an arrangement is provided for releasably locking the trim cylinder in its trimmed up position.
It is a further object of this invention to provide an improved automatically operated trim-up lock for the hydraulic power tilt and trim device of an outboard drive.
In addition to the aforenoted advantages, because the seal between the trim cylinder and the outer cylinder housing is at the lower end of this housing, then a long tool and intricate machining operation is required. Since it is desirable to maintain close tolerances in this area, this difficulty in machining gives rise to added costs for the prior art type of constructions.
It is, therefore, a still further object of this invention to provide an improved tilt and trim cylinder arrangement wherein the closely machined surfaces can be easily formed.